Silver halide emulsion containing acrylic amphoteric polymers

ABSTRACT

Amphoteric polymers prepared by polymerization of (a) acrylic acid, (b) N,N-dimethyl- or N,N-diethylaminoethyl methacrylate and, optionally, (c) esters of methacrylic or acrylic acid prepared by (i) emulsion polymerization of (b), (c) and the methyl ester of (a), followed by basic hydrolysis, or (ii) polymerization of (a), (b) and (c) in the presence of a strong acid, and photographic emulsions comprised of said polymers in which the molar ratio of (a) to (b) is at least 2 to 1 and a silver halide.

This is a division of application Ser. No. 07/343,773, filed Apr. 27,1989, U.S. Pat. No. 5,011,898, which was a division of application Ser.No. 07/076,806 filed on Apr. 1, 1988, U.S. Pat. No. 4,756,669 which wasa division of application Ser. No. 377,373 filed on May 12, 1982 U.S.Pat. No. 4,749,762.

FIELD OF THE INVENTION

This invention relates to acrylic amphoteric polymers and in the use ofcertain such polymers as photographic gelatin replacements or extenders.

BACKGROUND INFORMATION

Synthetic amphoteric polymers are useful in various applications, oftenas protein substitutes. Sterling, U.S. Pat. No. 4,075,131, discloses aconditioning shampoo containing a zwitterionic polymer which may beprepared by direct polymerization of acidic and basic monomers, e.g.,acrylic acid and a dialkylaminoalkyl methacrylate.

Matsudaira et al., U.S. Pat. No. 3,985,698, disclose an acrylic resinfor paints prepared from ethylenically unsaturated monomers havingtertiary amine groups, e.g., N,N-diethyl- and N,N-dimethylaminoethylmethacrylate; ethylenically unsaturated monomers having carboxyl groups,e.g., acrylic acid; and acrylate or methacrylate esters.

Samour, U.S. Pat. No. 3,790,533, discloses pressure sensitive adhesivepolymers comprised of certain carboxylic acid vinyl monomers, e.g.,acrylic acid; an aminoalkyl acrylate or methacrylate, e.g.,dimethylaminoethyl methacrylate; and an alkyl acrylate. Anderson et al.,U.S. Pat. No. 3,853,803, disclose similar amphoteric polymers which areuseful for producing crosslinkable, electrodepositable films and atechnique for direct polymerization of these monomers with minimalreaction between the amino and carboxyl groups.

Synthetic amphoteric polymers have been used in photographic silverhalide emulsions. Hollister et al., U.S. Pat. No. 3,749,577, disclosesuch a use for polymers prepared by direct polymerization of monomershaving a carboxyl functionality, e.g., acrylic acid, and monomers havinga quaternary ammonium functionality. U.S. Pat. No. 3,813,251 disclosessuch a use for similar polymers having a tertiary ammoniumfunctionality.

Flint et al., U.S. Pat. No. 4,293,635, disclose a photosensitivecomposition comprising an amphoteric polymer which is an interpolymer ofalkyl acrylamides, methacrylamides, aminoalkyl acrylates ormethacrylates; acids, including acrylic and methacrylic acids; andacrylate or methacrylate esters.

Klein, U.S. Pat. No. 3,950,398, discloses water-soluble acid additionsalts of methacrylic acid and 2-mono-(lower)alkyl-aminoethylmethacrylate in a molar ratio of 1.5:1 to 1:1.5. The salts can behomopolymerized to prepare amphoteric polymers or copolymerized.

Miyazako et al., U.S. Pat. No. 3,957,492, disclose a photographicemulsion which contains an amphoteric copolymer havingmorpholinyl-substituted alkylacrylamide groups and carboxylic metal saltgroups and which can be used as a partial or complete gelatinreplacement.

Smith et al., U.S. Pat. No. 3,692,753, disclose a silver halide emulsioncomprising amphoteric polymers of, e.g., N,N-dimethyl- andN,N-diethylaminoethyl methacrylate, acrylic acid, and acrylamides oracrylates having thioalkyl groups in the alkyl chain.

In U.K. Patent Specification 889,760 are disclosed light-sensitiveemulsions comprising amphoteric polymers prepared by hydrolysis ofpolymers containing groups capable of producing acidic and basic groupson hydrolysis.

Azorlosa, U.S. Pat. No. 2,592,107, discloses that amphoteric polymerscan be prepared by hydrolysis of polymers of amines containing a vinylradical or an N-acyl derivative thereof and vinyl, vinylidene orvinylene compounds containing potential acid-forming groups, e.g.,esters of acrylic acid.

Shachat et al., U.S. Pat. No. 3,689,470, disclose a method of preparingpolymers which contain a betaine-type group by direct polymerization ofa tertiary amine-containing monomer and acrylic acid or aqueous methylacrylate.

DISCLOSURE OF THE INVENTION

For further comprehension of the invention and of the objects andadvantages thereof, reference may be had to the following descriptionand to the appended claims in which the various novel features of theinvention are more particularly set forth.

The invention resides in an amphoteric polymer comprised of thefollowing monomers:

(a) acrylic acid,

(b) N,N-dimethylaminoethyl methacrylate, or N,N-diethylaminoethylmethacrylate and, optionally,

(c) a C₁₋₈ alkyl acrylate or methacrylate, 2-hydroxyethyl acrylate ormethacrylate or 2-hydroxypropyl acrylate or methacrylate,

prepared by (i) polymerization, preferably emulsion polymerization, ofmonomers (b) and, optionally, (c) and the methyl ester of (a) followedby selective hydrolysis of the resulting prepolymer or (ii)polymerization of (a), (b) and, optionally, (c) in the presence of astrong acid in a quantity sufficient to protonate the amine group of(b).

The amphoteric polymers prepared by said processes are substantiallyfree of any betaine-type contaminant. Therefore, the invention can alsobe said to reside in an amphoteric polymer comprised of monomers (a),(b) and (c) which is substantially free of betaine-type contaminants.

The invention also resides in a photographic emulsion comprising saidamphoteric polymer in which the molar ratio of (a) to (b) is at least 2to 1 and a silver halide and in the above-described processes forpreparing the amphoteric polymers of the invention.

By "comprises" is meant that the presence of other components which donot significantly adversely affect the invention are not precluded,e.g., sensitizers, surfactants, stabilizers and dyes. By "resultingprepolymer" is meant the preliminary polymer obtained by polymerizationof monomers (b) and, optionally, (c) and the methyl ester of (a), whichis selectively hydrolyzed to the amphoteric polymer of the invention.

The amphoteric polymers (polyampholites) of the invention are useful inphotosensitive compositions such as are used in photoresistapplications. The polymers in which the molar ratio of (a) to (b) is atleast 2 to 1 are useful as extenders and complete replacements forgelatin in photographic emulsions. The degree of polymerization ispreferably about 50 to 300. Many of these polymers provide an increasein covering power when so used. Covering power is a measure of theamount of silver halide needed to produce an image. It is the reciprocalof the photometric equivalent, pE, which is equal to M/D, M being themass of silver per unit area and D being the optical density, usuallymeasured as diffuse density. Such polymers are preferably comprised of20 to 90 mol % of (a), 10 to 30 mol % of (b) and 0 to 70 mol % of (c).Polymers in which the molar ratio of (a) to (b) is at least 2.5 to 1 arepreferred because when used in a photographic emulsion, they are morereadily redispersed in water at pH 6 after isoelectric precipitation atpH 4.

When tertiary amine-containing monomers are directly polymerized withacrylic or methacrylic acid monomers by conventional processes,betaine-type compounds are readily produced resulting in contaminationof the polymer with such compounds. The reaction yielding suchbetaine-type compounds is described by Shachat et al., U.S. Pat. No.3,689,470.

The amphoteric polymers of the invention can be prepared in two steps.First, a mixture of monomers (b) and (c) and the methyl ester of (a) arepolymerized to yield an acrylate-containing prepolymer. Second, theacrylate ester groups are selectively hydrolyzed, in the presence of abase, to yield the amphoteric polymer of the invention having pendantcarboxyl and dialkylaminoalkyl ester groups. This two-step procedure isan improvement in the polymerization of the monomers because theresultant polymer is substantially free of any betaine-type contaminant.

Preferably, the polymerization step is carried out by emulsiontechniques because the reaction proceeds more rapidly in this mannerthan by solution techniques. Emulsion polymerization can be carried outby known procedures, preferably using potassium persulfate as thepolymerization initiator. Polymerization temperature is preferably about50° to 70° C. although with a redox initiator system, e.g., potassiumpersulfate/N,N-dimethylaminoethanol, temperatures as low as about 0° C.can be used. The polymerization can be accomplished by batch orcontinuous processes. An expanding batch process with specific, gradual,controlled addition of monomer, initiator and emulsifier solution, and acontinuous overflow process are preferred. Such procedures are morefully described in the Examples below.

During the hydrolysis step, acrylate ester groups are rapidly convertedto carboxylate salt groups in the presence of a base. Since thishydrolysis reaction is several orders of magnitude faster than thecorresponding hydrolysis of methacrylate ester groups, selectivehydrolysis of the acrylate ester groups can be achieved. If a limitingquantity of base is used, hydrolysis will proceed only until the base isconsumed. Hence the degree of prepolymer hydrolysis and therefore theratio of carboxyl to dialkylaminoalkyl groups in the amphoteric polymercan be regulated by the relative quantity of base used.

Basic hydrolysis of the prepolymer is preferably carried out withaqueous potassium hydroxide, preferably in about a 10 to 20 percentsolution of the base and preferably at a temperature of about 65° to 90°C. Neutralization of the hydrolyzed polymer can be accomplished with astrong acid, e.g., nitric acid, and the polymer can be separated fromsolution by isoelectric precipitation in excess water. The amphotericpolymer can be redissolved, after purification, at a pH other than theisoelectric point. Alternatively, polymer neutralization can beaccomplished with an acidic ion-exchange resin. Slightly less than thecalculated amount of resin is usually employed to facilitate separationof the amphoteric polymer solution which can be used directly, ifdesired.

Alternatively, the amphoteric polymers of the invention can be prepareddirectly in one step by polymerizing a mixture of the monomers insolution in the presence of a strong acid. The acid protonates the aminegroups of (b), converting said groups to ammonium groups. Carrying outthe polymerization of the monomers in the presence of the acid is animprovement in the polymerization because the ammonium groups do notform betaine-type compounds. Therefore, the polymer is substantiallyfree of betaine-type compounds.

Useful acids include, for example, nitric acid, sulfuric acid andhydrochloric acid. A sufficient quantity is used to protonate the aminegroups of (b). The polymerization is preferably carried out at about 50°to 70° C., using potassium persulfate as the initiator. As in thetwo-step procedure, the polymerization can be accomplished by batch orcontinuous processes. Preferably, (b) is added to the acid to insurecomplete protonation prior to addition of (a) and (c).

EXAMPLES

The following are illustrative examples of the invention in which allparts and percentages are by weight and all degrees are Celsius unlessotherwise noted. The preferred embodiments are described in Examples 3,19, 20 and 21. Polymer molecular weights are number average (M_(n)),weight average (M_(w)) and viscosity average (M_(v)) and were determinedby gel permeation chromatography.

Polymer isoelectric points (pI) were determined by titration of a dilutepolymer solution from the acidic and basic sides of the pI untilcloudiness was observed. The pI was taken as the halfway point betweenthe two cloud points. At the isoelectric point, the polymers are leastwater-soluble and precipitation of the polymers occurs.

All reactors and reservoirs were flushed with nitrogen, and solutionswere maintained under a nitrogen atmosphere.

EXAMPLE 1 Preparation of Polyampholite by Bulk Single Batch Procedure

Apparatus: A jacketed resin kettle reactor was fitted with a refluxcondenser, vibromixer stirrer, a thermometer and thermocouple probe, anda nitrogen addition tube.

Emulsifier and Initiator Solution: The emulsifier and initiator solutionconsisted of a mixture of 5.0 g of a phosphate ester anionic surfactantin acid form, pH=5, in 500 ml of water to which 0.5 g of potassiumpersulfate initiator had been added.

Feed Monomer: The feed monomer consisted of a mixture of 29 ml ofdimethylaminoethyl methacrylate (0.165 mole) and 104 ml of methylacrylate (1.153 moles).

Procedure-Polymerization: The emulsifier and initiator solution wascharged to the reactor and heated to 60°. Then the feed monomer wasadded. The polymerization reaction temperature increased to about76°-78°. The reaction was continued for 1 hour. The product emulsion wascoagulated by adding acetone until the emulsion broke. The coagulatedpolymer was decanted, washed with water and separated by filtration. Thepolymer was dissolved in 500 ml of ethanol to give a solution weight of753 g and a prepolymer yield, based on a solids content of 0.159 g/gsolution, of 120 g (96% yield). Anal. Calcd. for 6 to 1 molar ratio ofmethyl acrylate to dimethylaminoethyl methacrylate: C, 57.06; H, 7.58;N, 2.08. Anal. Found: C, 56.43; H, 7.70; N, 1.94. The analysis showsthat the molar ratio is 6.57 to 1.

A second batch of polymer was prepared by the same procedure. A total of701 g of solution was obtained, and a prepolymer yield, based on asolids content of 0.159 g/g solution, of 112 g (89%) was obtained. Anal.Found: C, 56.44; H, 7.60; N, 2.01. The analysis corresponds to a monomermolar ratio of 6.27 to 1 of methyl acrylate-dimethylaminoethylmethacrylate. The polymer batches were combined; M_(w) =48,600; M_(v)=44,000.

Hydrolysis of prepolymer: A 21.8 g sample of the combined polymers (180g of polymer solution) was partially hydrolyzed by heating with asolution of 8.6 g of potassium hydroxide in 100 ml of water at 80° for0.75 hour. The reaction mixture was cooled to room temperature andpartially neutralized to its pI by adding 38.3 g of an acidiccross-linked polystyrene sulfonic acid ion exchange resin having 2.4 meqH⁺ per gram resin. This amount of resin corresponded to 0.092 equivalentof acid per 0.154 equivalent of base. The resin was washed successivelywith nitric acid and water before use. The reaction mixture was stirredfor 30 minutes, filtered, and the polyampholite polymer solution wasbottled; pI=4.3. The solution pH was 6.7. The polymer obtainedcorresponded to a monomer molar ratio of 5/1.43/1 of acrylic acid/methylacrylate/dimethylaminoethyl methacrylate.

EXAMPLE 2 Preparation of (3.0/0.8/1) Acrylic Acid/MethylAcrylate/Dimethylaminoethyl Methacrylate Polyampholite by ExpandingBatch Procedure

Apparatus: A jacketed resin kettle reactor was fitted with a refluxcondenser, vibromixer stirrer, inlet tubes for addition of monomer,initiator, and emulsifier solutions, a thermocouple temperature probe,and thermometer. The reactor was also fitted with a drain tube to allowthe removal of product emulsion following the completion of each batch.Monomer, initiator, and emulsifier were contained in separatereservoirs. The emulsifier reservoir was preheated via a circulatingwater bath to heat the emulsifier to the ambient reactor temperaturebefore introducing it to the reactor. Monomer, initiator, and emulsifiersolutions were fed into the reactor by metering pumps.

Emulsifier Solution: The emulsifier solution consisted of a mixture of25 g of a phosphate ester anionic surfactant in acid form, pH=5.0, 25.0ml of dimethylaminoethanol (DMAE) and 2500 ml of distilled water.

Initiator Solution: The initiator solution consisted of potassiumpersulfate, 5.0 g, dissolved in 500 ml of water.

Precharge Balance Monomer: A molar ratio of 6.73/1.0 of methylacrylate/dimethylaminoethyl methacrylate was employed.

Feed Monomer: A molar ratio of 4.0/1.0 of methylacrylate/dimethylaminoethyl methacrylate was employed.

Feed Pump Rates: The following pump rates were employed: monomerpump=3.56 ml/min; initiator pump=1.48 ml/min; emulsifier transferpump=13.35 ml/min.

Procedure-Polymerization: Emulsifier solution, 500 ml, was placed in thereactor. The remainder was placed in the preheated emulsifier reservoirand both solutions were heated to 65°. When the temperature stabilized,the initiator pump was started and allowed to run for 10 min to providea steady state radical concentration in the reactor. Such steady stateconcentration is achieved by constant addition of potassium persulfateto an excess of DMAE present in the reactor.

Precharge monomer, 50 ml, was added to the reactor. Immediatelyfollowing the injection of the precharge monomer, the feed monomer pumpwas started. The temperature profile of the reaction was followed usinga thermocouple and stripchart recorder. The temperature immediatelydropped upon addition of the precharge monomer but rapidly recovered andcontinued to climb to a plateau of 68° where it remained throughout thereaction. For best results, it is important to correlate monomer feedrate with reaction rate.

After 125.0 g (134 ml) of monomer had been fed (1/4 of total feedmonomer), the monomer pump was stopped and the product emulsion wasdumped over ice. The initiator pump was allowed to continue pumpingduring this cycle. The reactor was then refilled with 500 ml ofemulsifier solution from the reservoir and the reaction sequencedescribed above was repeated three times. The combined product emulsionswere coagulated by adding acetone followed by additional water. Thecoagulated prepolymer was decanted, washed with water, and dissolved in1 liter of ethanol for conversion to polyampholite. A total of 562 g ofsolid prepolymer was obtained. Anal. Found: C, 56.83; H, 7.67; N, 2.85.Elemental and infrared analyses showed that the polymer contained amonomer molar ratio of 3.8/1 of methyl acrylate/dimethylaminoethylmethacrylate. M_(n) =22,000; M_(w) =62,500; M_(v) =58,500.

Hydrolysis: The prepolymer solution obtained in the polymerization stepwas transferred to a 4 liter resin kettle fitted with a blade stirrer,reflux condenser, thermometer, and addition funnel. The mixture washeated to 80° with a hot water bath. When the temperature stabilized,198 g (3.54 moles) potassium hydroxide dissolved in 1000 ml water wasadded over a 1 hour period. This was the calculated amount of potassiumhydroxide needed to hydrolyze 2.8 of 3.8 methyl acrylate molecules permolar segment in the prepolymer. The reaction was continued for anadditional 1 hour. Then the reaction mixture was cooled to roomtemperature.

The basic polymer solution was partially neutralized to its pI by adding1064 g of the acidic ion exchange resin of Example 1. This amount ofresin corresponded to 2.20 equivalents of acid per 2.80 equivalents ofbase. The reaction mixture was stirred for 40 minutes, filtered, and thepolyampholite polymer solution was bottled. Total product solution, 2640g; solids content, 0.174 g polymer/g solution; total polyampholite, 459g; pI, 4.15. Anal. Found: C, 54.90; H, 7.19; N, 3.05.

EXAMPLE 3 Preparation of (4/1/1) Acrylic Acid/MethylAcrylate/Dimethylaminoethyl Methacrylate Polyampholite by ContinuousOverflow Procedure

Apparatus: A jacketed resin kettle reactor was fitted with a nitrogeninlet, thermometer, and thermocouple probe to record the thermal profileof the reaction, a vibromixer stirrer, inlet tubes from monomer,emulsifier, and initiator pumps, and an overflow tube which could beadjusted in height to allow the reaction mixture to overflow at theappropriate level into a product reservoir. The overflow tube for thisreaction was set to accommodate a 500 ml hold-up volume. Monomer,emulsifier and initiator solutions were pumped into the reactor fromseparate reservoirs.

Emulsifier Solution: The emulsifier solution consisted of a mixture of30 g of a phosphate ester anionic surfactant in acid form, pH=5.0, 30 mlof DMAE and 3000 ml of distilled water.

Initiator Solution: The initiator solution consisted of potassiumpersulfate, 5.0 g, dissolved in 250 ml of water.

Precharge Balance Monomer: A molar ratio of 9.6/1.0 of methylacrylate/dimethylaminoethyl methacrylate was employed.

Feed Monomer: A molar ratio of 5.0/1.0 of methylacrylate/dimethylaminoethyl methacrylate was employed.

Feed Pump Rates: The following initial pump rates were employed: monomerpump=5.34 ml/min; initiator pump=1.85 ml/min; emulsifier solutionpump=12.44 ml/min.

Procedure-Polymerization: Emulsifier solution, 500 ml, was charged tothe reactor. The remainder of the emulsifier solution was placed in thepreheated reservoir. The reactor was heated to 65°. Feed monomer wasplaced in the monomer reservoir. The initiator solution was placed inthe initiator reservoir.

When the temperature of the emulsifier solutions in the reactor andreservoir stabilized, the initiator pump was started and allowed to runfor 10 minutes to allow a stabilized radical concentration to beestablished in the reactor. Potassium persulfate reacts rapidly withDMAE as a redox couple to produce radicals at a rate which is severalorders of magnitude faster than through direct thermal decomposition ofpersulfate.

The reaction was started by injecting 35 ml of the precharge monomer tosaturate the emulsion solution with monomer having a ratio ofacrylate/methacrylate necessary to produce prepolymer with the desired5/1 composition. This injection was immediately followed by the start ofthe monomer pump feeding monomer plus a small amount of prechargebalance monomer. The rate of feed of monomer is equal to the rate ofpolymerization to form product for the specific conditions of theparticular reaction and monomer combination. The emulsifier pump wasstarted simultaneously with the monomer pump at a rate selected tomaintain an emulsifier solution/monomer solution ratio of 2.33/1. Thisratio produces a 25% solids level of polymer in the product emulsion.The reaction was followed by monitoring the thermal profile of thereaction using a thermocouple probe and a stripchart recorder.

The reaction temperature rose to 68° within 6 minutes after start of thereaction and it then leveled off and dropped slightly. An injection of0.5 ml of methyl acrylate to the reactor helped to stabilize thetemperature during polymerization. A thermal plateau was maintaineduntil monomer solution in the reservoir had been depleted. A rapiddecrease in temperature indicated that polymerization was complete.

The product was collected in four fractions. The first was taken duringestablishment of the thermal plateau and the time period during whichthe solids level was increasing to 25%. This was equal to 22 minutes,the turnover time for the holdup volume of the reactor at the pump ratesused. Fractions 2 and 3 were collected at 50 minutes and at the end ofmonomer addition, respectively. Fraction 4 was the emulsion whichremained in the reactor at the completion of the polymerization.

Each fraction of product emulsion was coagulated by adding acetonefollowed by water. The coagulated product was washed extensively withwater. Fractions 2, 3 and 4 were combined and dissolved in 1500 ml ofethanol in preparation for conversion of prepolymer to polyampholite. Atotal of 2114 g of polymer solution was obtained; solids content, 0.225g polymer/g solution; total prepolymer, 476 g; infrared analysis showeda monomer ratio of 4.7/1, and C--H--N analysis showed a monomer ratio of4.82/1 of methyl acrylate/dimethylaminoethyl methacrylate in thepolymer: M_(w) =19,000; M_(v) =18,000.

Hydrolysis: The prepolymer solution obtained in the polymerization stepwas transferred to a 4.0 liter resin kettle reactor fitted with a bladestirrer, a reflux condenser, and a 1 liter addition funnel. The mixturewas heated by a constant temperature bath to 78°. To this mixture wasadded, over a 45 minute period, 174 g of potassium hydroxide (3.12moles) dissolved in 1000 ml of water. Following this addition, themixture was heated for 1 hour and then cooled to room temperature. Thebasic polymer solution was partially neutralized to its pI by adding1069 g of the acidic ion exchange resin used in Example 1. This quantityof resin corresponded to neutralization of 3.0 of the 3.7 moles ofcarboxylate groups formed during hydrolysis. The reaction mixture wasfiltered to remove the resin, and the polyampholite polymer solution wasbottled and sampled for analysis. Total product solution, 3056 g; solidscontent (after the solution was concentrated to reduce the alcoholconcentration to 12.8%), 0.141 g polyampholite/g solution; pI, 4.05;solution pH, 6.0.

EXAMPLES 4 TO 20

The preparative procedures used in Examples 4 to 20 are summarized inTables I and II, below. Example 17 was carried out substantially by theprocess of Example 1; Examples 7 and 9, by the process of Example 2; andExamples 4 to 6, 8, 10 to 16 and 18 to 20, by the process of Example 3.The initiator solution consisted of 3 g of potassium persulfatedissolved in 3000 ml of water except that in Example 7, the amounts were5 g in 5000 ml; in Example 9, the amounts were 2 g in 500 ml; in Example17, the amounts were 1 g in 1000 ml; in Example 18, the amounts were 20g in 300 ml; and in Examples 19 and 20, the amounts were 5 g in 250 ml.

                  TABLE I                                                         ______________________________________                                                     Precharge             Pump                                                    Balance    Monomer    Rate                                       Emulsifier   Monomer    Feed       ml/min(4)                                  Ex.   Solution(1)                                                                              Ratio(2)   Ratio(3) I   M   E                                ______________________________________                                         4(6) 15/0/3000  23/7.4/12.3                                                                              169/100/165                                                                            (5) 1.9 8.5                               5    15/0/3000  68.4/0/11.6                                                                              323/0/105                                                                              (5) 2.0 6.4                               6    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                               7    25/25/2500 --         361/0/176                                                                              4   0.8 3.0                               8    30/0/3000  24.6/0/8.6 336/0/196                                                                              (5) 1.5 4.7                               9    25/25/2500 --         362/0/176                                                                              4   0.8 3.0                              10    15/0/3000  33.8/0/8.8 289/0/141                                                                              (5) 1.5 6.6                              11    15/0/3000  33.8/0/8.8 289/0/141                                                                              (5) 1.5 6.6                              12    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                              13    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                              14    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                              15    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                              16    30/0/3000  27.9/0/5.1 407/0/120                                                                              (5) 1.1 3.4                              17    10/0/1000  --         208/0/58 (5) --  --                               18    25/25/2500 29.0/0/6.0 475/0/169                                                                              6   2.0 4.0                              19(7) 25/25/2500 29.0/0/6.0 475/0/169                                                                              5   1.9 3.8                              20(8) 25/25/2500 29.0/0/6.0 475/0/169                                                                              5   1.9 3.8                              ______________________________________                                         Notes                                                                         (1) The emulsifier solution is stated as the g of phosphate ester anionic     surfactant in acid form/ml DMAE/ml distilled water.                            (2) The precharge balance monomer ratio is stated as the ratio, in ml, o     methyl acrylate/methyl methacrylate/dimethylaminoethyl methacrylate unles     otherwise noted.                                                              (3) The monomer feed ratio is stated as the ratio, in ml, of methyl           acrylate/methyl methacrylate/dimethylaminoethyl methacrylate unless           otherwise noted.                                                              (4) The pump rates are shown for initiator solution (I), monomer solution     (M) and emulsifier solution (E).                                              (5) The initiator solution was combined directly with the emulsifier          solution.                                                                     (6) A total of 1.5 ml of lauryl mercaptan was added to the feed monomer.      (7) A total of 1.0 ml of lauryl mercaptan was added to the feed monomer       and 0.1 ml to the precharge monomer.                                          (8) A total of 1.0 ml of bromotrichloromethane was added to the feed          monomer and 0.1 ml to the precharge monomer.                             

                  TABLE II                                                        ______________________________________                                                                       Acidic                                              Pre-                      Ion Ex-                                             polymer   Monomer         change                                              Hydrolyzed                                                                              Molar     KOH   Resin                                          Ex.  g         Ratio(1)  g     g      Mv    pI                                ______________________________________                                         4   398       2/1/1     104   141    41,000                                                                              5.3                                5   36.6      3/1.46/1  11.4  56.5   --    4.4                                6   38.6      4/1.28/1  14.1  52.6   --    4.25                               7   344       2.8/1/1   112   740    --    4.2                                8   282       2/0.65/1  84    548    --    5.0                                9   242       2.5/0.7/1 78    467    --    4.5                               10   41.9      2.0/0.85/1                                                                              11.7  65.0   12,000                                                                              4.7                               11   41.9      2.85/0/1  16.6  86.7   12,000                                                                              4.2                               12   38.6      2/3.28/1  7.1   39.4   10,000                                                                              4.85                              13   38.6      2.5/2.78/1                                                                              8.8   52.6   10,000                                                                              4.8                               14   38.6      3.0/2.28/1                                                                              10.6  52.6   10,000                                                                              4.6                               15   38.6      4.0/1.28/1                                                                              14.1  52.6   10,000                                                                              4.25                              16   38.6      5.28/0/1  18.7  65.7   10,000                                                                              3.9                               17   21.8      5/1.43/1  8.6   38.3   45,000                                                                              4.3                               18   68.5      4/1.2/1   22.7  116    28,000                                                                              4.0                               19   392       3.6/1/1   141   751    60,000                                                                              4.4                               20   392       3.4/0.7/1 141   751    54,000                                                                              4.0                               ______________________________________                                         Notes                                                                         (1) The monomer molar ratio is given as the ratio of acrylic acid/methyl      (meth)acrylate/dimethylaminoethyl methacrylate in the polyampholite.     

EXAMPLE 21 Preparation of (4/1/1) Acrylic Acid/MethylAcrylate/Dimethylaminoethyl Methacrylate by Direct Polymerization inAcid Solution Apparatus

A jacketed resin kettle reactor was fitted with a blade stirrer, anaddition funnel, a reflux condenser, and a nitrogen inlet. The apparatuswas heated by a constant temperature bath.

Procedure

Water (500 ml) and 17 ml of 70% nitric acid were placed in the reactorand heated to 65°. Dimethylaminoethyl methacrylate (29.6 g; 0.189 mole)was then added, and the solution was mixed to insure completeprotonation of the amine groups. A mixture of the other two monomers,acrylic acid (54.2 g; 0.753 mole) and methyl acrylate (16.2 g; 0.188mole) was then added with stirring. The initiator solution of 1.0 g ofpotassium persulfate in 100 ml of water was added slowly through theaddition funnel over a 2-hr period. Heating was continued for anothertwo hours before the reaction was terminated. During the reaction periodthe mixture increased in viscosity but remained clear.

The viscous polymer solution was diluted with water, and 20% sodiumhydroxide solution was added to increase the pH to 4.5 (isoelectricpoint) to precipitate the polymer. The polymer was decanted, washed withwater (pH 4.5), and again decanted.

A 17.15 g sample of the 4/1/1 copolymer was dissolved in water, pH 6.0,to give 490 g of solution; solids content, 0.0350 g polymer/g solution;solution pH, 7.3; pI, 4.2.

As noted above, certain of the amphoteric polymers of the invention inwhich the molar ratio of acrylic acid monomer/dialkylaminoethylmethacrylate monomer is at least 2/1 are useful in increasing thecovering power of silver halide photographic emulsions when they areemployed as gelatin extenders or replacements for gelatin. The followingprocedures illustrate this utility by employing the polymers inconventional balanced double jet and two stage single jet precipitationof silver iodobromide crystals. Covering power (C.P.) is defined asoptical density divided by developed silver coating weight per unitarea, that is, D/M.

PROCEDURE A

Monodisperse silver iodobromide crystals were grown on a 1.5-mole scaleby balanced double jet precipitation using the amphoteric terpolymer ofExample 4 as a protective colloid. As a control, such crystals weregrown in the same manner using gelatin as the protective colloid. Theconditions and resultant crystal size in each case are shown in TableIII.

                  TABLE III                                                       ______________________________________                                                       Gelatin   Amphoteric                                                          (Control) Terpolymer                                           ______________________________________                                        Quantity         45 g        10 g                                             NH.sub.4 OH (0.88 s.g.)                                                                        1 ml        2.25 ml                                          Temperature      46.1°                                                                              54.4°                                     Crystal Size     0.0041 μm.sup.3                                                                        0.0042 μm.sup.3                               (number average)                                                              ______________________________________                                    

The water soluble salts were removed by coagulation of the emulsions. Inthe gelatin control, this was achieved by adding a negatively chargedpolymer, polyvinyl alcohol-o-sulfobenzaldehyde, and lowering the pH to2-3. After thorough washing, the coagulated material was redispersed byvigorous stirring at pH 6. In the case of the amphoteric polymer,lowering the pH to 4.8 alone caused coagulation. Redispersion waseffected by applying ultrasound at pH 6.

In both cases, the emulsion was prepared in the same way. Gelatin (83g/mole Ag) was added and the crystals were fogged with cesiumthiodecaborane and Au³⁺ at 72° for 2 hours at pH 7.6. The pH was thenlowered and surfactant, formaldehyde and a desensitizing dye were addedjust prior to coating at 2.6 g Ag/m² on a gelatin-subbed polyester base.Both emulsions showed direct positive response on exposure, but thecrystals containing the amphoteric terpolymer showed significantlyhigher covering power under three different development conditions assummarized in Table IV.

                  TABLE IV                                                        ______________________________________                                                       C.P. (m.sup.2 /g)                                                               Amphoteric Gelatin                                           Development Conditions                                                                         Terpolymer (Control)                                         ______________________________________                                        A.sup.(1), 35°, 90 sec, tray                                                            1.83       1.49                                              A.sup.(1), 42°, 20 sec,                                                                 1.91       1.63                                              machine processor                                                             B.sup.(2), 27°, 90 sec,                                                                 1.62       1.42                                              machine processor                                                             ______________________________________                                         .sup.(1) A continuous tone Nmethyl-p-aminophenol sulfate/hydroquinone         developer was used.                                                           .sup.(2) A lithographic hydroquinone developer was used.                 

PROCEDURE B

Monodisperse silver iodobromide crystals were grown on a 0.38-mole scaleby balanced double jet precipitation using the amphoteric terpolymer ofExample 5. The precipitation conditions were identical to those used inProcedure A, and crystals with a number average particle size of 0.0045μm³ were obtained. Coagulation, washing, and redispersion were carriedout as in Procedure A. The amphoteric polymer coagulated at pH 4.0, andvigorous stirring gave complete redispersion. Gelatin was added to theemulsion which was then fogged and coated using the conditions ofProcedure A. The emulsion was overcoated with an anti-abrasion layercontaining additional formaldehyde. The direct positive emulsion gave aC.P. of 1.79 m² /g when tray-developed with the continuous toneN-methyl-p-aminophenol sulfate/hydroquinone developer used in ProcedureA at 35° for 90 seconds.

A control experiment in which the amphoteric terpolymer was replacedwith gelatin and the resultant emulsion was identically developed gavesilver halide crystals which had significantly lower covering power,namely, 1.37 m² /g.

PROCEDURE C

Monodisperse silver iodobromide crystals were grown on a 1.5-mole scaleby balanced double jet precipitation using the amphoteric terpolymer ofExample 6 as the protective colloid. The precipitation conditions wereidentical to those used in Procedure A, and crystals with a numberaverage particle size of 0.0054 μm³ were obtained. The emulsion wascoagulated, washed, redispersed, fogged and coated as in Procedure B,and a formaldehyde-containing overcoat was applied. The direct positiveemulsion gave a covering power of 1.84 m² /g when developed as inProcedure B. Hence the amphoteric terpolymer-grown crystals, despitetheir larger size, showed much higher covering power than thegelatin-grown control of Procedure B.

PROCEDURE D

Large silver iodobromide crystals were grown on a 3-mole scale by atwo-stage single jet precipitation with physical ripening after eachstage using the amphoteric terpolymer of Example 7 as a protectivecolloid. As a control, such crystals were grown in the same manner usinggelatin as the protective colloid. The conditions and resultant crystalsize in each case are shown in Table V.

                  TABLE V                                                         ______________________________________                                                      Gelatin   Amphoteric                                                          (Control) Terpolymer                                            ______________________________________                                        Quantity        40 g        12 g                                              Temperature     41°  42°                                        NH.sub.4 OH (.88 s.g.)                                                                        75 ml       75 ml                                             Ripening Times  5 & 6 min   7 & 8 min                                         Crystal Size    0.78 μm.sup.3                                                                          0.85 μm.sup.3                                  (volume average)                                                              ______________________________________                                    

Coagulation, washing and redispersion steps were carried out asdescribed in Procedure B. Gelatin (87 g/mole Ag) was added and thecrystals were digested for 30 min at 69° with gold, sulfur, andthiocyanate sensitizers. Wetting agents and antifoggants were added andthe emulsions were coated onto a gelatin-subbed polyester base at acoating weight of 2.9 g Ag/m² along with an overcoat containingformaldehyde and chrome alum hardeners. The emulsions were exposed toDmax and developed in a Kodak Xomat® M6-AN automatic processor using DuPont XMD medical X-ray developer (33°, 19 seconds). The amphotericpolymer-grown crystals showed slightly higher covering power (0.75 m²/g) than the gelatin-grown controls (0.72 m² /g) despite the larger sizeof the amphoteric polymer-grown crystals.

PROCEDURE E

Large silver iodobromide crystals were grown on a 3-mole scale under thesame conditions described in Procedure D using the amphoteric terpolymerof Example 8 or a gelatin control as the protective colloid. Crystalswith volume weighted size of 0.38 μm³ were obtained with the amphotericterpolymer, and crystals of 0.41 μm³ were obtained with gelatin. Theemulsions were coagulated, washed, redispersed, and sulfur and goldsensitized as described in Procedure D. They were then coated ontogelatin-subbed polyester base at a coating weight of 3 g Ag/m², and aformaldehyde-containing overcoat was applied. The films were exposed anddeveloped as in Procedure D. The C.P. of the terpolymer-grown crystalswas 0.72 m² /g which was slightly higher than the C.P. of thegelatin-grown controls which was 0.70 m² /g.

PROCEDURE F

Large silver iodobromide crystals were grown in gelatin and sensitizedas described in Procedure D. A sample (0.23 mole Ag) of this emulsionwas split into three equal portions. Nothing was added to portion #1,1.2 g of extra gelatin was added to portion #2, and 1.2 g of theamphoteric terpolymer of Example 7 was added to portion #3. Theemulsions were all coated at 2.9 to 3.7 g Ag/m² onto gelatin-subbedpolyester base, and a formaldehyde-containing overcoat was applied.After aging for 10 days to allow hardening of the emulsion layer, thefilms were exposed to Dmax and developed as described in Procedure D.The C.P. of the various films was measured, and the results aresummarized in Table VI.

The results show that addition of the amphoteric terpolymer as a gelatinextender gives a substantial increase in silver halide covering power.

                  TABLE VI                                                        ______________________________________                                        Film            C.P. (m.sup.2 /g)                                             ______________________________________                                        #1 - (Control)  0.65                                                          #2 - (Control)  0.64                                                          #3 -            1.00                                                          ______________________________________                                    

PROCEDURE G

Large silver iodobromide crystals were grown in gelatin and sensitizedas in Procedure D. A sample (0.18 mole Ag) of this emulsion was splitinto three equal portions. Nothing was added to portion #1, 1 g of theamphoteric terpolymer of Example 9 was added to portion #2, and 2 g ofthe same terpolymer was added to portion #3. The emulsions were coatedas in Procedure D, and an overcoat layer containing chrome alum andformaldehyde hardeners was applied. The films were exposed to Dmax anddeveloped as in Procedure D. The C.P. of the various films was measured,and the results are summarized in Table VII.

                  TABLE VII                                                       ______________________________________                                        Film            C.P. (m.sup.2 /g)                                             ______________________________________                                        #1 - (Control)  0.46                                                          #2              0.56                                                          #3              0.61                                                          ______________________________________                                    

The results show that addition of the amphoteric terpolymer to themedical x-ray emulsion resulted in a significant increase in coveringpower.

PROCEDURES H-P

Monodisperse silver iodobromide crystals were grown on a 0.38-mole scaleby balanced double jet precipitation using the polyampholites listed inTable VIII as protective colloids. In each experiment, 2.5 g of thepolyampholite, 0.55 ml of 0.88 s.g. ammonium hydroxide, a temperature of54°, and a pH of 8.0 were employed for the precipitation. The crystalsizes (number average) obtained, V, are shown in the table.

                  TABLE VIII                                                      ______________________________________                                        Procedure   Polyampholite of Example                                                                       V, μm.sup.3                                   ______________________________________                                        H            4               0.017                                            I           10               0.012                                            J           11               0.015                                            K           12                0.0070                                          L           13                0.0064                                          M           14                0.0065                                          N           15               0.011                                            O           16               0.014                                            P           17               0.021                                            ______________________________________                                    

While the preferred embodiments of the invention are illustrated by theabove, it is to be understood that the invention is not limited to theprecise construction herein disclosed and that the right to all changescoming within the scope of the invention as defined by the followingclaims is reserved.

I claim:
 1. Photographic emulsion, comprising:A. an amphoteric polymer containing the following monomeric units:(a) 20 to 90 mol percent of acrylic acid, (b) 10 to 30 mol percent of N,N-dimethylaminoethyl methacrylate of N,N-diethylaminoethyl methacrylate, and (c) 0 to 70 mol percent from one or more members of the group consisting of C₁₋₈ alkyl acrylate, C₁₋₈ alkyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; said polymer prepared by copolymerizing (a), (b), and (c), in solution, in the presence of a strong acid selected from the group consisting of nitric acid, sulfuric acid and hydrochloric acid, in a quantity sufficient to protonate the amine group of (b), the polymer characterized further by having (i) a molar ratio of (a) to (b) of at least 2 to 1, and (ii) substantially no betaine contaminant; and B. a silver halide.
 2. The photographic emulsion as recited in claim 1 wherein said amphoteric polymer has a degree of polymerization of 50 to
 300. 3. The photographic emulsion as recited in claim 1 wherein the ratio of (a) to (b) in said amphoteric polymer is at least 2.5 to
 1. 4. The photographic emulsion as recited in claim 2 wherein the ratio of (a) to (b) in said amphoteric polymer is at least 2.5 to
 1. 5. Photographic emulsion, comprising:A. an amphoteric polymer containing the following monomeric units:(a) 20 to 90 mol percent of the methyl ester of acrylic acid, (b) 10 to 30 mol percent of N,N-dimethylaminoethyl methacrylate or N,N-diethylaminoethyl acrylate, and (c) 0 to 70 mol percent of units from one or more members of the group consisting of C₁₋₈ alkyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; said polymer prepared by copolymerizing (a), (b), and (c), and then hydrolyzing the polymer in aqueous base to selectively convert acrylate ester groups to carboxylate salt groups, thereby forming the amphoteric polymer characterized by:(i) molar ratio of hydrolyzed polymer units derived from monomer (a) which contains carboxylate salt groups, to monomer (b), of at least 2 to 1, (ii) a degree of polymerization of about 50 to 300, and (iii) substantially no betaine contaminant; and B. a silver halide.
 6. The photographic emulsion as recited in claim 5 wherein the ratio of hydrolyzed (a) units to (b) units in said amphoteric polymer is at least 2.5 to
 1. 